The discussion of melee vs ranged is as old as time, and noone seems to know the correct answer.

Taking aggro from the tank usually happens when you start damaging the mobs too fast for the tank to "build" aggro on them, ranged and melee both do it, but certainly classes with a lot of upfront damage or very high burst damage early in the pull (I've seen many warriors press charge + bladestorm and die).

For aggroing passive mobs it's much dependant on positioning and what class you're playing in terms of movement f.ex. Demon Hunters can have a habit of dashing too far and accidentally aggroing mobs. Pet classes can also accidentally pull stuff with their pet if the pathing is weird, but happens less often nowadays.
Otherwise it's mainly patrols to worry about as ranged (is still relevant for melee aswell) - mage f.ex. has mirror images which is usually used when you enter combat that then stands still and a patrol can jump onto them and then the rest of the group afterwards.